Spring Trap is the main antagonist of Five Nights at Freddy's 3. Springtrap is a prototype animatronic suit, retrofitted for both endoskeletons and humans. However, the suit's springlocks were loose and easily malfunctioned, causing the suit to contract and tighten if they did and potentially crushing humans if they were inside. For this reason, Springtrap was abandoned in place of the current animatronic suits and left to rot, however, the creators of Fazbear's Fright found the suit and decided to use it as an animatronic, unknowing of its sentience.

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At the end of the 5th night, it is revealed that Springtrap was the suit that Purple Guy attempted to get into upon being cornered by the spirits of Freddy Fazbear and the others. While he did succeed hiding in the suit, he failed to crank it properly, and the suit tightened, its inner workings mangling the killer's body and crushing him to death. The Killer died within Springtrap and his corpse remained within (as showed within multiple images that may be shown when starting up the game). The Killer still remains within Springtrap in the years of Fazbear's Fright and his spirit likely haunts the suit similarly to the murdered children.

At the end of the 6th and final night, Alphonse Elric burns the entire building to the ground for a good reason, and Springtrap himself is destroyed for good along with it.

even though the newspaper article mentioned that the remaining parts of anything found within the attraction would later be auctioned off. When the image is brightened, Springtrap's head can be seen in the background, and Alphonse Elric is holding his head as a message to stop making horror attractions based on the yet to be solved mysteries of Freddy Fazbear's Pizza.
In sisters location at the ending it reveals springtrap is still alive as he jumps up from the ruins of freddy fazbears pizza.